1. Field of the Invention
The present invention relates to a system, apparatus, and method for the collection of friction ridge signatures from a subject. More particularly, the present invention relates to a low power consumption, small size, and low weight friction ridge capturing device and method for the collection of friction ridge signatures from a subject. Most particularly, the present invention relates to a low power consumption, compact, and portable digital friction ridge capturing apparatus, system and method for the collection of friction ridge signatures with a platen area of at least 3.0 square inches.
2. Description of the Related Art
Human beings have friction ridges on their hands and feet. Friction ridge impressions from a subject's fingers are commonly known as fingerprints. Animals also commonly have unique friction patterns on their footpads. In dogs and cats, for example, these patterns are called paw prints.
Digital scanning systems that capture friction ridge impressions, collectively termed herein as ‘fingerprints’, are old in the art. Many of these systems were designed to capture a smaller area of one or two fingerprints while others were designed to capture a much larger area. Such existing systems commonly use optical imaging, capacitance, infrared radiation, ultrasound, or other means to capture fingerprints.
Many optical imaging systems are designed to capture one or two fingerprints at a time. These systems are termed ‘single print devices’ herein. For example, the manufacturers listed in Table 1 provide optical devices that scan one or two fingerprints at a time.
TABLE 1NameWeb AddressCross Match Technologieshttp://www.crossmatch.comExact IDhttp://www.exactid.com/Identixhttp://www.identix.com/Secugenhttp://www.secugen.com
Devices that capture a single fingerprint at a time are compact and draw minimal power during operation. One of the first issued patents that discloses how such a single digit device works is U.S. Pat. No. 3,200,701 to White, the entire contents of which is hereby incorporated by reference as if fully set forth herein. White teaches a device that uses a light source, a prismatic body, the principle of Total Internal Reflection “TIR”, and a scanning apparatus to capture a fingerprint image. A typical TIR scanning system that captures fingerprint images comprises a light source, a prism, a camera, and a host computer or other control device that is used to capture the image. It should be understood that the camera is any type of suitable sensor for the capture of image data. This includes Charge Coupled Devices (CCD) and Complimentary Metal Oxide Semiconductor (CMOS) cameras as well as sensor chips included in these cameras and both linear and area scan versions. The host computer or other control device is referred to as a host computer. There may be other components of a prior art system such as, e.g., polarizing filters, corrective optics, and holographic gratings.
Most commercially available large format optical systems today follow this single digit system configuration. That is, they use a light source, prismatic body, TIR, camera(s), and host computer to create fingerprint images. For prior art devices, “capable of capturing more than two fingerprints simultaneously” means optical devices having a surface capture area exceeding 3.0 square inches. This type of system is referred to as a large format fingerprint capture system. In addition, large format fingerprint capture systems include those that capture palm prints and writer's edge.
Large format fingerprint devices typically capture fingerprints from multiple fingers simultaneously and therefore, the area upon which the subjects place their fingers must be large enough to accommodate the maximum number of fingers to be captured simultaneously. Usually, this number is four, but Cross Match Technologies provides a system that is able to capture the fingerprints in two groups of two fingerprints apiece. In effect, this Cross Match Technologies system captures four fingerprints simultaneously.
Livescan systems, one common form of large format fingerprint system, typically use a glass or plastic surface, termed a platen, upon which the subject's fingers are rolled or pressed. Images of the fingers' ridges are typically captured from underneath the platen by one or multiple cameras and are then converted into digital files. Images of rolled fingers are called rolled prints and images of pressed fingers are called slaps. Livescan devices are available from the sources listed in TABLE 2.
TABLE 2NameWeb AddressCross Match Technologieshttp://www.crossmatch.comHeimann Biometric Systemshttp://www.hbs-jena.com/Identixhttp://www.identix.com/Printrakhttp://www.printrakinternational.com/
A large body of patents exists for large format fingerprint scanning devices. U.S. Pat. No. 3,200,701 to White, discussed above, discloses one such system. Further, U.S. Pat. No. 4,933,976 to Fishbine et al., the entire contents of which are hereby incorporated by reference as if fully set forth herein, teaches a configuration comprising a prismatic-based TIR device for fingerprint capture. Fishbine et al. disclose a method that combines successively captured images into one image array.
U.S. Pat. Nos. 5,548,394, 5,629,764, 5,650,842, 6,178,255, and 6,407,804 all disclose variations of the TIR based prismatic platen device used to capture fingerprint images.
In U.S. Pat. No. 5,548,394 to Giles et al., the entire contents of which are hereby incorporated by reference as if fully set forth herein, teaches a TIR based system that uses a linear CCD camera (as opposed to an area based camera) and associated optics that is used to create rolled fingerprints. Prints are captured by changing the orientation of a mirror as a scan progresses.
U.S. Pat. No. 5,629,764 to Bahuguna et al., the entire contents of which are hereby incorporated by reference as if fully set forth herein, teaches correcting the aspect ratio of images using holographic gratings. Light incident on the fingerprint surface is totally internally reflected at the surface of the prism but immediately after being reflected back toward the prism the light enters a holographic grating that changes the light direction. Light, directed now at the hypotenuse of the prism at an angle greater than the critical angle, is total internally reflected toward the camera. In this patent, the aspect ratio is corrected before the light leaves the prism.
U.S. Pat. No. 5,650,842 to Maase et al., the entire contents of which are hereby incorporated by reference as if fully set forth herein, discloses a fingerprint capture system that optically corrects the aspect ratio of images after the image beam leaves the prism. Correction is achieved by including optical elements in the image path after the image exits the prism. The image may be generated using TIR or light dispersion from the friction ridges. A reference light source is an edge lit light panel manufactured by Hewlett-Packard that is illuminated by red Light Emitting Diodes (LEDs).
U.S. Pat. No. 6,178,255 Scott et al., the entire contents of which are hereby incorporated by reference as if fully set forth herein, discloses a method and apparatus in which a mechanism slides a prism over an imaged area of a camera. By using a linear encoding mechanism, the method and apparatus splices together complete fingerprint images from the smaller portions of the fingerprint that are captured when sliding the prism over the camera.
U.S. Pat. No. 6,407,804 to Hillman et al., the entire contents of which are hereby incorporated by reference as if fully set forth herein, discloses a fingerprint capture system with embedded reference targets in the optical path. Using these reference targets, the system can be calibrated at anytime using these internal reference targets. This patent also discloses use of a planar light source constructed from a two dimensional array of LEDs followed by a diffusor.
Several patented systems do not teach that TIR be used at the fingerprint imaging surface in order for a fingerprint to be captured. Such systems are disclosed in U.S. Pat. Nos. 5,621,516, 5,650,842 and 6,061,463.
U.S. Pat. No. 5,621,516 to Shinzaki et al., the entire contents of which are hereby incorporated by reference as if fully set forth herein, discloses a system that images randomly reflected light from the friction ridges. By providing means of minimizing the light content reflected by platen areas not in contact with the friction edges, the contrast of the resulting images are improved. U.S. Pat. No. 5,650,842 to Maase et al., discussed above, provides another mechanism for capture of friction ridges via light dispersion.
U.S. Pat. No. 6,061,463 to Metz et al., the entire contents of which are hereby incorporated by reference as if fully set forth herein, teaches using a slanted-fringed light diffractive grating to redirect light perpendicularly toward the platen surface. Light reflected from the surface is then captured by the camera. Light incident upon the friction ridges is dispersed and therefore this less intense reflection is imaged as dark. One disclosed embodiment uses volume holograms to redirect light. This patent contrasts with U.S. Pat. No. 5,629,764 to Bahuguna et al. in that this patent redirects the light before it reaches the platen surface and therefore image aspect correction is never required.
Based on the foregoing discussion, most, if not all, existing commercial large format fingerprint devices use the principle of TIR. In the majority of these devices, the object plane to be imaged (the fingerprint) and the image plane of the camera are not parallel, centered, and perpendicular to a common axis. To correct for optical perspective distortions introduced by the relative positions of the object and image planes optics within the device must correct the positions of the object and/or image planes before the camera captures an image or the system must employ an algorithmic solution for correcting the perspective distortion introduced into the image. In the first case, if additional optical components are added, the size and weight of the device increase. For example, see U.S. Pat. Nos. 5,650,842 and 6,407,804. In the later cases, to avoid an unfocused image the depth of field must be deep enough for the entire object area to be in focus. Since the image is not optically corrected for perspective distortion, the depth of field requirement is driven by the three dimensional geometry of the platen, the optics used between the platen surface and the camera, and the geometric relationship between the camera and the platen surface. Typically, lenses that allow larger depths of field have focal lengths such as 30 mm or greater with corresponding f-stops often greater than 4.0. Long focal length lenses often result in a distance from the object plane to the image plane that is too large to put the entire device into a physically compact solution. In addition, high f-stop lenses restrict the amount of light entering a camera and therefore more light, power, and/or exposure are needed for these systems, thus implying a larger power consumption.
Often aberrations in the periphery of the image such as barrel distortion and pincushion distortion distort the fingerprint to the point where the images are not truly usable. Barrel distortion occurs when the distance of the pixels along the image edges are farther away from the center of the image than the corresponding actual distance in the target. Pincushion distortion occurs when the pixels along the images edges are closer to the center of the image that the corresponding actual distance in the target. Barrel and pincushion distortions are introduced via lenses used in an optical system and both distortion types may be present at the same time.
The majority of existing optical fingerprint systems rely on LEDs for light sources. Light illuminating the platen may be either diffuse or collimated.
Electricity consumers in a fingerprint device include the light source(s), the camera(s), frame grabber electronics, magnetic stripe readers, barcode readers, radio frequency identification modules, proximity card readers, smartcard readers, displays, platen heaters, platen blowers, and servomotors, if present. In total, the power used by such systems is above 10 watts for all existing large format fingerprint systems. Therefore, prior art large format fingerprint devices are powered by external power sources connected via separate cabling since power provided over a single data/control/power cable will either be insufficient or the battery on the attached computer will be drained too quickly. In other words, prior art systems cannot be powered only from the computer to which the device is attached.
Most of the patented systems described above are either not compact or not lightweight and therefore they cannot be considered as portable. To be moved, these devices often require a protective case. In existing instances, the device and case weigh over 30 pounds. In addition, many devices must be re-calibrated once the device has been moved and reinstalled. Such re-calibration is required due to the presence of moving parts or the possibility that parts have moved relative to one another.
Such systems also commonly address the issue of condensation on the platen. Such condensation occurs when the dew point around the platen/finger is too high relative to the ambient temperature of the prism and therefore moisture from the finger condenses on the prism. In such cases, platen heaters and platen blowers have been used to minimize the condensation effects to the image.
No prior art large format fingerprint scanning device has the ability to pass all data, power, and control logic over a single physical connection to the device. In addition, image-processing means to identify the start and stop points of a fingerprint image capture session also do not currently exist. Rather, external controls such as foot pedals, touch screens, keyboard keys, and buttons located on the device are commonplace as means to identify start and stop points for capturing fingerprint images.